Two-stroke combustion engines are widely used in hand-held power tools. Typically, a two-stroke combustion engine includes an air filter provided in a suction channel of the engine. The air filter is essential to ensure a proper operation of the engine. The air filter traps the dust and other particulate matter present in the combustion air and provides clean air to the engine. Typically, an air filter includes an interior chamber, one or more filter elements and a suction opening for connecting the air filter to the suction channel of the engine. During operation of the engine, the combustion air flows through the one or more filter elements into the interior chamber and further, passes through the suction opening into the suction channel of the engine.
As well known in the art, in the two-stroke combustion engine, the suction channel is further connected to a crankcase or a cylinder. During operation of the engine a mixture of unburned fuel and lubricant present in the crankcase may flow back into the suction channel. The back flow of the mixture of unburned fuel and lubricant from the crankcase into the suction channel is referred as back flow or back spit. In case of a two-stroke combustion engine, where no system is provided to control the back flow or back spit, the mixture of unburned fuel and lubricant may clog and plug the air filter prematurely and hence, the air filter needs be cleaned or replaced very frequently.
Typically, the cost of the air filter is low, and its replacement is a small additional bother that is addressed along with other maintenance work. However, in case of power tools which are used in dusty environments, such as high performance applications, industrial and farming applications, the cost of air filter replacement may be significant, and thus a significant increase in filter performance and lifespan may be required. In the prior art, in order to minimize the back flow, valves may be used in the crankcase and/or the suction channel. However, the design and installation of such valves is reasonably complicated and expensive.
Therefore, there is a need for a means for improving the service life of two-stroke combustion engines and specifically of the air filters by controlling the back flow in two-stroke combustion engines. Moreover, there is a need for a means for controlling the flow of the combustion air in a suction direction of the air filter.